Abstract: 【Aim】 The green peach aphid, Myzus persicae, is an important crop pest distributed worldwide. This pest has developed resistance to a variety of chemical pesticides in recent years. The purpose of this study is to screen Lecanicillium strains with high virulence against M. persicae and excellent performance in cultivation. 【Methods】 Seven strains of two Lecanicillium species, namely three strains of L. psalliotae (HFLP006, HFLP021 and HFLP025) and four strains of L. attenuatum (HFLA032, HFLA041, HFLA064 and HFLA066), were selected, and the colony growth and spore production of these strains cultivated on SDAY plates were observed. The lethality and the medium lethal time (LT₅₀) of these strains against the apterous adults of M. persicae were measured by immersion method using a 2.0×10⁷ conidia/mL spore suspension, and the medium lethal concentration (LC₅₀) values of HFLP006 and HFLA032 strains were determined with a graded series of concentrations of spore suspension (1.0×10⁴-1.0×10⁸ conidia/mL). The symptoms of apterous adults infected by HFLP006 strain at the concentration of 1.0×10⁸ conidia/mL spore suspension were observed under stereoscopic microscope. 【Results】 The colony morphology of the seven strains of Lecanicillium on the SDAY plate was basically similar. The HFLP006 and HFLA032 strains showed better growth and spore-producing traits, with the colony diameter of 50.75 and 51.13 mm, and the spore yields of 13.90×10⁷ and 11.50×10⁷ conidia/cm², respectively, at 15 d after inoculation. The spore germination rates of all the strains were above 96.00%, with the HFLP006 strain showing the germination rate of 99.28%. The HFLP006 strain also displayed the highest pathogenicity against the apterous adults of M. persicae, causing an 83.56% corrected accumulative mortality at 7 d after treatment, which was significantly higher than those caused by the other fungal strains. Moreover, the LT₅₀ value of the HFLP006 strain against the apterous adults of M. persicae was 3.74 d, which was significantly lower than those of the other strains. The HFLA032 strain also had good performance against the apterous adults of M. persicae, causing a corrected accumulative mortality of 63.01% and a LT5₀ of 5.75 d against the apterous adults of M. persicae. Furthermore, virulence determination revealed that the LC₅₀ values of HFLP006 and HFLA032 strains against the apterous adults of M. persicae at 7 d after treatment were 0.21×10⁶ and 1.86×10⁶ conidia/mL, respectively. The HFLP006 strain at a concentration of 1.0×10⁸ conidia/mL spore suspension impaired the vitality of M. persicae adults on the 2nd day after treatment, and brown spots were observed on the abdomen of aphid body. Then the thorax and abdomen became brown, the legs and antennae became white, and the whole body became very wizened. Finally, a large amount of white filamentous hyphae grew out from aphid body. 【Conclusion】 The HFLP006 strain is a candidate biological control agent against M. persicae since it causes the highest mortality and the shortest lethal time against the apterous adults of M. persicae. In addition, the HFLP006 strain shows an excellent cultivation performance on SDAY medium. The results of this study provide a theoretical basis for further largescale fermentation of this fungal strain.

Key words: Myzus persicae; Lecanicillium; Lecanicillium psalliotae; Lecanicillium attenuatum, colony morphology, pathogenicity, biological control